This invention relates to an optical waveguide array having lens, in which a refractive index is distributed two-dimensionally, and also relates to a method for manufacturing the optical waveguide array. The optical waveguide array is, for example, used for an optical scanning unit mounted on a laser printer.
Optical scanning units using an optical waveguide array and mounted on the laser printer are known in the art and, for example, one is shown in FIG. 13. The optical scanning unit in FIG. 13 uses an optical waveguide array 95. A semiconductor laser 91 emits light beams. The light beams pass through an image-forming lens member 93, and are deflected by a polygonal mirror 94 which is rotating at a constant speed. The light beams deflected by the polygonal mirror 94 are propagated from an incidence portion 95A through the optical waveguide array 95, are emitted from an irradiation portion 95B, and are then focused on a lens array 97. Subsequently, the light beams are scanned on a photosensitive drum 96, which is rotating at a constant speed, in the direction parallel the rotational axis of the photosensitive drum 96, as shown by an arrow E. The lens array 97 focuses the light beams emitted from the irradiation portion 95B in the direction traverse with and perpendicular to the scanning direction shown by the arrow E. As shown in FIG. 12, without the lens array 97, however, the light beams would diverge from the irradiation portion 95B by angle .theta.c. The angle .theta.c is determined by the numerical aperture NA of the optical waveguide array 95 according to the equation of .theta.c=sin.sup.-1 (NA). In this case, the spot diameter of the light beams irradiated on the surface of the photosensitive drum 96 is thus enlarged, thereby impairing the resolution of a latent image formed on the surface of the photosensitive drum 96. To improve the resolution of the latent image, the related art shown in FIG. 13 has the lens array 97 inserted between the irradiation portion 95B of the optical waveguide array 95 and the photosensitive drum 96, so that the light beams emitted from the irradiation portion 95B are focused on the surface of the photosensitive drum 96. The lens array 97 is very expensive, thereby adding to the cost of the optical scanning unit.